Soybean Cultivars Resistant and Susceptible to Heterodera glycines

Additional tests of 178 cultivars and lines of soybean against soybean cyst nematode are reported. Cultivars are available with some level of resistance to races 1, 2, 3, 4, 5, 6, 9, and 14, but in some cases the resistance level is moderate. No cultivar or line (except possibly PI 437654) has resistance to all of the races tested. Thirteen cultivars and lines, however, were resistant or moderately resistant to race 1, 14 to race 2, 87 to race 3, 2 to race 4, 3 to race 5, 42 to race 6, 18 to race 9, and 36 to race 14. Some have resistance to more than one race.

Benomyl Tolerance of Ten Fungi Antagonistic to Plant-parasitic Nematodes

Ten strains of fungi were tested for tolerance to the fungicide benomyl. Verticillium chlamydosporium strain 2 did not grow in the presence of benomyl; Drechraeria coniospora strains 1 and 2 and Chaetomium sp. tolerated only 0.1 mug benomyl/ml medium; Acremonium bacillisporum, an unidentified fungus, and Phoma chrysanthemicola uniformly grew at 1 mug/ml, but some hyphae grew at higher benomyl concentrations; Fusarium sp. tolerated 475 mug/ml, but some hyphae grew on medium amended with 1,000 mug/ml; Verticillium lecanii and V. chlamydosporium strain 1 routinely tolerated 1,000 mug/ml. Fungi generally grew more slowly at higher than at lower benomyl concentrations. Strains with elevated tolerance to benomyl were selected from Acremonium bacillisporum, Drechmeria coniospora, Fusarium sp., and an unidentified fungus. These strains retained the increased tolerance after repeated transfers on unamended medium.

Rotations of soybean with tropical corn and sorghum for the management of nematodes

The relative efficacy of rotations of soybean with sorghum and tropical corn for nematode management was studied for 2 years in a field infested with root-knot (Meloidogyne arenaria) and soybean cyst (Heterodera glycines, race 14) nematodes. Corn, sorghum, and soybean cv. Kirby were planted in 1989, and in 1990 the same areas were planted with seven soybean cultivars with and without at-plant application ofaldicarb. Corn and sorghum did not support H. glycines, but significant juvenile populations of the nematode in soil were associated with Kirby soybean. Numbers of H. glycines and M. arenaria juveniles in 1990 depended on cultivar and cropping system but were little affected by nematicide treatment. Lowest numbers of H. glycines juveniles were associated with Leflore soybean and the corn-soybean rotation. Numbers of M. arenaria juveniles were highest with Leflore and lowest with Braxton and Brim soybean. The sorghum-soybean rotation resulted in slightly higher numbers of M. arenaria juvenile populations than soybean monoculture or the corn-soybean rotation. Aldicarb increased yields of some cultivars, but its use was not justified economically. Yields of all cultivars were from 19-287% higher in rotation systems than in monoculture.

Resistance in Soybean Cultivars from Maturity Groups V-VIII to Soybean Cyst and Root-knot Nematodes

One hundred thirty-nine cultivars of soybean (Glycine max) in Maturity Groups V, VI, VII, and VIII were evaluated in a greenhouse for resistance to Heterodera glycines races 3 and 14 and Meloidogyne incognita, M. arenaria, and M. javanica. Of the cultivars tested, 37% had resistance to H. glycines race 3 alone, 12% had resistance to both races 3 and 14, and 69% exhibited a moderate or high level of resistance to one or more of the Meloidogyne spp. However, 24% were susceptible to each race of H. glycines and to all Meloidogyne spp. Whereas 40% of the cultivars were moderately resistant to M. javanica, only 23% were moderately resistant to M. incognita and 24% to M. arenaria. Although 28% of the cultivars had a high level of resistance to M. incognita, only 6 and 3% had this level of resistance to M. javanica and M. arenaria, respectively. Seventeen percent of the cultivars possessed a moderate or high level of resistance to all three Meloidogyne spp., and 37 % had resistance to H. glycines race 3 and M. incognita. With the exception of resistance to H. glycines race 14, resistance in soybean to these nematodes was fairly uniformly distributed across maturity groups.

Evaluation of Two Soybean Cultivars and Aldicarb Treatment in Soil Infested with Plant-parasitic Nematodes

The soybean cultivars Davis and Leflore were grown in a northern Florida experimental site infested with eight species of plant-parasitic nematodes. Meloidogyne incognita appeared to become the predominant pathogen, suppressing Davis soybean yield regardless of aldicarb treatment. Soybean yields of Leflore were 1.4-fold to 3.5-fold greater than yields of Davis, but aldicarb did not affect yields of either cultivar. Davis soybean yield was negatively correlated with the at-plant density of M. incognita, whereas Leflore seed yield was not negatively correlated with any nematode.

Distribution of Heterodera glycines Races in Illinois

Because the race scheme for Heterodera glycines was expanded recently from 5 to 16 races, the occurrence and distribution of races in Illinois need clarification. Forty-four populations of H. glycines were collected from sites in 23 of the 88 infested counties. Populations were tested using the differential soybean lines Pickett 71, Peking, PI 88788, and PI 90763. Lee 68 and Williams 82 were used as standards. Seedlings were grown in 7.5-cm-d clay pots and inoculated with 1,000 eggs and second-stage juveniles obtained from H. glycines-infested field soil. Plants were maintained in a greenhouse at 22-28 C. After 1 month, the number of first-generation white females that developed on each differential was determined and the race of the population was designated. Twenty-eight populations were race 3, twelve were race 1, two were race 5, one was race 2, and one was race 4. Populations of races 3 and 1 were widely distributed in the state. In 26 of the 28 race determinations, race designations using Williams 82 and Lee 68 were the same, indicating that if Lee 68 is not available, Williams 82 may be a suitable alternative for race tests done in the north central United States.

Response of Soybean Cultivars to Aldicarb in Heterodera glycines-infested Soils in Missouri

Soybean cultivars in maturity groups III, IV, and V that were resistant or susceptible to Heterodera glycines were evaluated for their response to in-furrow applications (5.43 kg a.i./ha) of aldicarb. Tests were conducted over three years (1988-1990) in various H. glycines-infested locations in Missouri for a total of 16 environments. In 7 environments, overall yields were higher (P </= 0.05) in aldicarb-treated than in nontreated plots. In one environment, soybean yields in aldicarb-treated plots were lower (P </= 0.05) than in nontreated plots. Cultivar x aldicarb interactions were detected in only one environment. Resistant cultivars yielded higher than susceptible cultivars in 13 of 15 environments. Final populations (Pf) of H. glycines were generally unaffected by aldicarb treatment; however, in 3 environments Pf were significantly higher, whereas in 2 other environments Pf were significantly lower in aldicarb-treated plots than in nontreated plots.

Characteristics and Efficacy of a Sterile Hyphomycete (ARF18), a New Biocontrol Agent for Heterodera glycines and Other Nematodes

A filamentous, nonsporulating fungus, designated Arkansas Fungus 18 (ARF18), was isolated from 9 of 95 populations of Heterodera glycines, the soybean cyst nematode, in Arkansas. In petri dishes, ARF18 parasitized 89% of H. glycines eggs in cysts. The fungus also infected eggs of Meloidogyne incognita and eggs in cysts of Cactodera betulae, H. graminophila, H. lespedezae, H. leuceilyma, H. schachtii, and H. trifolii. In pot tests, reproduction of SCN was 70% less in untreated field soil that was naturally infested by ARF18 than in autoclaved field soil. Although ARF18 grew well at 25 C on cornmeal agar over a wide pH range, it did not sporulate on 28 media and thus could not be identified to genus or species.

Management of Heterodera glycines by Cropping and Cultural Practices

Heterodera glycines was identified in North Carolina in 1954, although symptoms of the disease were noted in the state at least 8 years earlier. Crop rotation experiments designed to develop management systems were initiated in 1956. Two or more years in production of a nonhost crop resulted in decreases of the nematode to low or undetectable levels with acceptable subsequent yields of soybean (Glycine max). Because of almost complete dependence on resistant cultivars and (or) nematicides for nematode control, crop rotation experiments were not conducted from 1962 to 1980. Research on control of H. glycines, beginning in 1981, emphasized biological and ecological aspects of the nematode in order to determine cropping systems that restrict the nematode to nondamaging levels. Mortality during embryogenesis was high at temperatures above 30 C. Hatching of eggs occurs readily in May and June. Postinfection development takes 2-3 weeks at weekly mean temperatures of 22-29 C and is slow above and below those temperatures. Egg production is high during the late growing season. Some cultural practices such as planting early maturing cultivars in mid-to-late June and rotation with a nonhost effectively keeps populations at low levels.

Control of the soybean cyst nematode by crop rotation in combination with a nematicide

An experiment to evaluate the control of soybean cyst nematodes compared 1-year, 2-year, and 3-year nonhost rotations with continuous soybeans (Glycine max) in 0.2-ha plots. In a second 1-year rotation, the plots were planted to soybean or corn (Zea mays) after fumigation in the spring with a split application of 1,3-dichloropropene (748.2 liters/ha). The effects of the nematicide were apparent the first year. Soybean yield was 1,482 kg/ha compared to 233 kg/ha in the untreated plots. In the second year, the highest yielding plants (2,035 kg/ha) were those following 1 year of corn that had been treated the previous year; plants in untreated plots yielded 288 kg/ha. Average yield of soybean following 1 year of corn was 957 kg/ha compared to 288 kg/ha for continuous soybean. In the third year, the effects of the nematicide were still evident. Soybean plants in plots treated the first year, followed by corn, then soybean, yielded 1,044 kg/ha compared to 761 kg/ ha for soybean following 1 year of corn and 991 kg/ha for soybean following 2 years of corn. Plots planted to soybean for 3 consecutive years yielded 337 kg/ha. Nematicidal effects were no longer evident during the fourth year. Yields were most improved by the greatest number of years in the nonhost crop; highest yields in descending order were from plants following 3 years of corn, 2 years of corn, and 1 year of corn. Plots planted to soybean for 4 consecutive years yielded 130 kg/ha. Highly significant negative correlations occurred each year between initial nematode population densities and seed yield.

Optimization of the Heterodera glycines Race Test Procedure

Effects of pot size, length of seedling radicle at the time of inoculation with Heterodera glycines, transplanting after inoculation, type and amount of inoculum, and temperature were tested to determine the optimum procedure for the H. glycines race test. Numbers of H. glycines females extracted from plants in 7.5-cm-d pots tended to be higher than numbers from 10-cm-d pots, but not significantly so. Radicle lengths from 2.5 cm to 7.5 cm had no effect. Transplanting after inoculation reduced the variation in the number of females extracted, but the numbers of females produced were very low. Plump females (40 per pot) or eggs (4,000 per pot) were the best inocula. A constant temperature of 28 C appeared to be optimum. More H. glycines females were extracted from plants 28 days after inoculation than at 35 days. Race tests in which all of these factors were included were still highly variable in the number of H. glycines females extracted from different replications of the same test host. Tests of several susceptible cultivars revealed differences in their capabilities as hosts of H. glycines races.

Influence of Selected Plant Species on Hatching of Eggs and Development of Juveniles of Heterodera glycines

The influence of selected plant species on egg hatch and subsequent development of Heterodera glycines race 3 was investigated. Plants tested included four soybean cultivars, red clover, alfalfa, hairy vetch, field corn, sweet corn, cabbage, tobacco, cotton, and wheat. Soybean stimulated egg hatching more than any of the other plant species, with H. glycines-resistant cultivars being more stimulating than susceptible ones. Hairy vetch also increased hatch. Roots of cabbage, red clover, alfalfa, and hairy vetch were readily penetrated by juveniles of H. glycines. Maturation to adult occurred only on soybean and hairy vetch.

Interactions of Vesicular-Arbuscular Mycorrhizal Fungi, Phosphorus, and Heterodera glycines on Soybean

Effects of vesicular-arbuscular mycorrhizal (VAM) fungi and soil phosphorus (P) fertility on parasitism of soybean cultivars Bragg and Wright by soybean cyst nematode (SCN) were investigated in field micropiot and greenhouse experiments. VAM fungi increased height of both cultivars and yield of Wright in microplot studies in 1986 and 1987. Conversely, yield of mycorrhizal and nonmycorrhizal plants of both cultivars was suppressed by SCN. Soil population densities of SCN were unaffected by VAM fungi in 1986 but were greater in microplots infested with VAM fungi than in control microplots in 1987. Growth of Wright soybean was stimulated by VAM fungi and suppressed by SCN in greenhouse experiments. The effect of VAM fungi on SCN varied with time. Numbers of SCN in roots and soil were decreased by VAM fungi by as much as 73% at the highest SCN inoculum level through 49 days after planting. Later, however, SCN numbers were usually comparable on mycorrhizal and nonmycorrhizal plants. Soil P fertility generally had no effect on SCN. Results of a split-root experiment indicated that VAM fungal suppression of SCN was not systemic.

Interactions Between Calonectria crotalariae and Heterodera glycines on Soybean

The interactions of Heterodera glycines at four egg inoculum levels (0, 100, 1,000, and 10,000 per pot) and three cyst levels (0, 100, and 200 per pot) and Calonectria crotalariae at 500, 5,000, and 50,000 microsclerotia per pot were evaluated on soybean. At the two lowest nematode egg levels, the presence of C. crotalariae did not affect nematode reproduction. At 10,000 eggs per pot, however, nematode reproduction was increased significantly at each microsclerotial level. The increase in nematode reproduction was stepwise at 500 and 5,000 microsclerotia per pot but declined at 50,000 microsclerotia per pot. Similar results were obtained when cysts rather than eggs were used as nematode inoculum. The nematode x fungus interaction significantly affected 60-day plant growth parameters of both Lee 74 and Centennial soybean. The nematode x fungus interaction was antagonistic to plant roots and significantly influenced root injury ratings. The presence of C. crotalariae in tissues of stock plants or plants used as race differentials did not alter the analysis of this population as race 3.

Isolation of Fungi from Heterodera glycines and in vitro Bioassays for Their Antagonism to Eggs

Twenty fungi were assayed in vitro for antagonism to eggs of Heterodera glycines. Eight of the fungi were isolated from cysts or eggs of H. glycines during the current study, one was isolated from Panagrellus redivivus, and eleven were obtained from other researchers or collections. The bioassays were conducted on eggs from nematodes that had been grown monoxenically on excised root tips. Phoma chrysanthemicola, one strain of Verticillium chlamydosporium, and one strain of V. lecanii caused a decrease (P < 0.01, P < 0.05, P < 0.05, respectively) in the number of viable eggs, although no hyphae were observed colonizing live eggs. Trichoderma polysporum infected live eggs but enhanced (P < 0.05) egg survival. Acremonium bacillisporum, Chaetomium sp., Drechmeria coniospora (two strains), Epicoccum sp., Exophiala jeanselmei, Fusarium sp., Neocosmospora vasinfecta, Scytalidium fulvum, Trichoderma harzianum (two strains), V. chlamydosporium (one strain), V. lecanii (three strains), and an unidentified fungus did not measurably affect egg viability, even though hyphae of five of these fungi were seen in live eggs. The bioassay provides a useful step in the selection of a biological control agent for this major nematode pest.

Interaction of three plant-parasitic nematodes on corn and soybean

Interaction of Belonolaimus longicaudatus, Meloidogyne incognita, and Pratylenchus brachyurus on corn and B. longicaudatus, M. incognita, and Heterodera glycines on soybean was investigated in micropiots during two seasons for corn and one season for soybean. Changes in population densities and effects on plant growth of each nematode on corn or soybean alone and in mixed culture were compared. No interactions occurred on corn in 1987. In 1988, midseason population densities of B. longicaudatus were greater in corn plots infested with M. incognita (P </= 0.05), but at harvest, population densities or B. longicaudatus were less in corn plots infested with P. brachyurus (P </= 0.05). Except for stalk weight at harvest, plant growth was not affected by any treatment. In soybean, midseason densities of M. incognita were increased in combination with H. glycines (P </= 0.05), but this trend reversed at harvest. Soybean yield was reduced in plots infested with H. glycines (P </= 0.001), whereas B. longicaudatus or M. incognita had no effect on plant growth either singly or in mixed culture.

Evaluation of Thuringiensin for Control of Heterodera glycines on Soybean

The efficacy of ABG-6162A (1.5 L formulation of thuringiensin) for control of Heterodera glycines on soybean (Glycine max cv. Williams 82) was evaluated in the greenhouse at rates of 0, 10, 100, 500, and 1,000 ppm a.i. and in a field experiment at rates of 0, 3.4, 10.2, and 20.3 g a.i./100 m of row applied in an 18-cm-wide band. In the greenhouse, the 100-ppm rate was as effective as an equivalent rate of aldicarb and caused no phytotoxicity, but the higher rates of thuringiensin were highly phytotoxic. In the field experiment, numbers of females recovered from plots treated with thuringiensin at the 3.4-g and 10.2-g rates were greater (P </=0.05) than from plots treated with aldicarb at 20.3 g a.i./100 m of row in an 18-cm-wide band or from the H. glycines-resistant soybean cv. Fayette. Yield of the untreated Williams 82 control differed significantly only from the 10.2-g rate of thuringiensin, but yield of untreated Fayette was greater than that from any of the treatments involving Williams 82.

Repeated sampling to determine the precision of estimating nematode population densities

The first phase of this study involved repeated samplings of five fields using composite samples of 10, 20, 40, and 80 soil cores, to determine the precision of nematode assays. The second phase focused on randomly selecting two and four 2-ha subunits (data on Meloidogyne spp.) of 24 fields ranging from 6 to 40 ha and computing the precision of estimated means for these numbers ofsubunits versus the general field mean (based on all 2-ha subunits). Average numbers of nematodes from most samples containing Meloidogyne spp., Heterodera glycines, Helicotylenchus dihystera, Scutellonema brachyurum, and (or) Hoplolaimus galeatus were within 50% of the overall means. Coefficient of variation (CV) values were generally lower for 40 cores than for 10, 20, and 80 cores per sample. When data for all nematodes and fields were combined, this value was lowest for 40 and 80 cores. The CV values were higher for Meloidogyne spp. than for H. glycines. Means of two samplings increased the probability of obtaining numbers nearer the mean for that field than numbers from a single composite sample. For the second phase, population estimates of Meloidogyne spp. based on four 2-ha subunits generally were closer to field means than were those for two subunits. Sampling precision with these subunits diminished greatly in large fields with variable soils and (or) mixed cropping histories. Either two or four subunits gave population estimates within 3-20% of the field mean in most instances. The mean man hours required for sampling ca. 2-ha parcels of 4-20-ha fields was 0.54 hours.

Evaluation of Soybeans in Maturity Groups I-IV for Resistance to Heterodera glycines

Forty-seven private and public soybean (Glycine max) cultivars in maturity groups I, II, III, and IV were evaluated in the field for resistance to Heterodera glycines race 3 and race 4 at two sites, Kilbourne and Urbana, Illinois. The soil at Kilbonrne was an irrigated sand infested with race 3. The soil at Urbana was a nonirrigated silty clay loam infested with race 4. Yield of nematode-susceptible controls was reduced at both locations, and yield differences were observed among the other cultivars. Soybeans grown in sand yielded less than the soybean grown in silty clay loam. Although populations of H. glycines recovered at planting were lower at Kilbourne than at Urbana, a greater percentage of loss in yield was associated with the sand at Kilbourne. Several soybean cultivars had a high level of resistance to both populations of H. glycines.

Plant-parasitic Nematode Acetylcholinesterase Inhibition by Carbamate and Organophosphate Nematicides

The sensitivity of acetylcholinesterases (ACHE) isolated from the plant-parasitic nematodes Meloidogyne arenaria, M. incognita, and Heterodera glycines and the free-living nematode Caenorhabditis elegans to carbamate and organophosphate nematicides was examined. The AChE from plant-parasitic nematode species were more sensitive to carbamate inhibitors than was AChE from C. elegans, but response to the organophosphates was approximately equivalent. The sulfur-containing phosphate nematicides were poor inhibitors of nematode acetylcholinesterase, but treatment with an oxidizing agent greatly improved inhibition. Behavioral bioassays with living nematodes revealed a poor relationship between enzyme inhibition and expression of symptoms in live nematodes.

Demonstration of Multiple Mating in Heterodera glycines with Biochemical Markers

Controlled crosses of Heterodera glycines were carried out by placing one o r more virgin females of known esterase phenotype on an agar plate and adding, at various time intervals, one or more males of different esterase phenotypes. Progeny (second-stage juveniles) of such crosses were propagated on soybeans, and 30 days later young females were subjected to electrophoretic analysis to determine their esterase phenotype. Esterase phenotypes that represented the heterozygous state of the maternal and paternal genomes confirmed the hybrid nature of the progeny and identified their male parent. When each of 74 females was given the opportunity to mate successively with two males of different esterase phenotypes, 43 mated with a single male and 31 mated with both males. One female mated with three males, i.e., with a male of its own population (sib mating) and the two males provided for the cross. Inseminated females could mate for a second time soon after, or as late as 24 hours after, their first mating. When single males were given the opportunity to mate with many females, about equal numbers of them inseminated zero, one, two, or three females. In greenhouse tests, 12 females were given the opportunity to mate with many males of three different esterase phenotypes. Two females mated with one and possibly more males of the same phenotype, and 10 females mated with males of two different esterase phenotypes. In conclusion, multiple mating appears to be a common behavior of males and females of H. glycines.

Inability of a Seed Treatment with Pseudomonas cepacia to Control Heterodera glycines on Soybean

A commercial seed treatment containing Pseudomonas cepacia was applied to Glycine max cv. Williams 82 (susceptible to Heterodera glycines) and was compared to Fayette soybean (resistant to H. glycines) for control of H. glycines at two locations in Illinois. The soil at the first location was sandy in texture and the field was irrigated, whereas the soil at the second location was a silty clay loam and the field was not irrigated. At both locations there was no yield increase associated with the seed treatment , but yield of Fayette was significantly (P < 0.05) greater than Williams 82 regardless of treatment.

Survey of soybean cyst nematode races in tennessee

Cordell soybean is a newly released cultivar resistant to Heterodera glycines (SCN) races 3 and 5. The hectarage infested with these races and with other races that can parasitize Cordell in Tennessee is not known. A survey of races in Tennessee soybean fields with sampling weighted by soybean hectarage on a county basis was conducted in 1988. The SCN race plus female development on Bedford and Cordell soybeans were determined in a greenhouse for 21 field populations. Races 2, 3, 4, 5, 6, and 9 were 14%, 5%, 10%, 38%, 19%, and 14% of these populations, respectively. The SCN female indices on the differentials that were sources of SCN resistance in Bedford and Cordell were not accurate indicators of female development on these cultivars. The female index was < 10 on PI 90763 for 19 populations, but four of these populations had an index > 30 on Cordell, which derives SCN resistance from PI 90763. The index was < 10 on PI 88788 for seven populations, but two populations had an index > 40 on Bedford, which derives resistance from PI 88788. When recommending cultivars to be planted by soybean producers, SCN reproduction should be determined on the cultivars, instead of on race differentials.

Interaction Among a Nematode (Heterodera glycines), an Insect, and Three Weeds in Soybean

A 2 x 3 x 4 factorial field experiment was established to determine the interaction among a nematode, an insect, and three weed species on soybean in 1983-86. Low (nematicide treated) or high (untreated) population densities of the soybean cyst nematode (SCN), Heterodera glycines, and 0, 30, or 70% main stem girdling by the threecornered alfalfa hopper (TCAH), Spissistilus festinus, were combined with no weeds, one common cocklebur (CC), Xanthium strumarium, one sicklepod (SP), Cassia obtusifolia, or one pitted morningglory (PMG), Ipomoea lacunosa, per meter of row in all possible combinations. Most of the losses from the pests were significant (P </= 0.05) and additive. The high population density of SCN suppressed soybean seed yield by 14%. Girdling of 30 and 70% by TCAH suppressed yields by 10 and 25%, respectively. One CC, SP, or PMG per meter of row suppressed yield by 22, 14, and 12%, respectively. The addition of loss predictions for each pest was approximately the actual treatment losses recorded. The pests did not have an evident interactive effect on yield losses; however, the losses attributed to each pest were additive.